Seven-fold dynamical symmetry in solid-state nuclear magnetic resonance

Nuclear magnetic resonance is a very useful physical effect discovered independently by two groups of American scientists in the 1940's. These researchers discovered that if ordinary matter is placed in a strong magnetic field, radio waves with well defined frequencies, like radio stations, are absorbed or emitted. One group first detected this effect in a large block of wax; another used ordinary tap water. The radio emissions are due to the atomic nuclei that sit at the heart of every atom. Some of these atomic nuclei are magnetic, and it is the rotatory motion ("precession") of these microscopic magnets that cause the detectable radio signals